And be careful of the container you are using to spray the paint into. The first time I did it I transfered the spray paint into a plastic container. The next day I found a spectacular melted mess oozing off my workbench. I suggest only glass containers.
As others have suggested, let the paint sit in the OPEN, jar for a few hours. Overnight is usually enough. This is to let the propellent gas from the can release from the paint. When the jar no longer feels cool to the touch, you can cap the paint.
Don't thin the paint, just use it straight in your airbrush. At least that's been my experience.
You can decant primer as well as paint. I use Rust-Oleum American Accents primer. I think it works as well or better than Tamiya primer. It levels very well, does not cover detail, and bonds extremly well to the plastic. Walmart had a can of it (reddish-brown) on the discounted paint rack- $1.93!
Some paints seems to degrade over time (a few months??) after being decanted. I suggest decanting in quantities that you will use over the short term.